1. Field of the Invention
The present invention relates to a latch plate for a seat belt system. More specifically, the present invention relates to a breakaway latch plate that maintains seat belt webbing at a fixed position relative to the plate during normal usage, but allows movement of the seat belt webbing in accident conditions.
2. Technical Background
Seat belts are known to increase the safety of occupants in various motorized vehicles. Seat belt use is often cited as the most useful line of defense in reducing accident related injuries. The actions of consumer groups, governmental agencies, and political activists all reflect the tremendous societal value of seat belt use. Legislation requiring manufacturers to include seat belts in their vehicles has been in place for many years. More recently, laws have been enacted requiring consumers to use seat belts.
The benefits of seat belt use are numerous. In a collision, seat belts may prevent the occupant of a vehicle from striking the interior of the vehicle or other objects within the vehicle, including other occupants. Seat belts aid in keeping the occupant inside the vehicle, where the chances of survival are much greater. Seat belts may also keep the driver behind the wheel and in control of the vehicle in a collision, averting additional damage or injuries. Seat belts also enhance the effectiveness of other safety devices. For example, in a vehicle with airbags, a seat belt keeps the occupant in the seat, so the airbag can better protect the occupant.
Statistics show that lap and shoulder belts, when used properly, reduce the risk of fatal injury in front-seat occupants of cars by 45 percent and the risk of moderate-to-critical injury by 50 percent. With respect to light truck occupants, seat belts reduce the risk of fatal injury by 60 percent and moderate-to-critical injury by 65 percent.
Seat belts vary in their configuration, but one of the most common types of seat belts is the lap belt. The lap belt includes right and left belts, which traverse an occupant""s lap and are secured to each other by a buckle, which is often located near the occupant""s mid-abdomen. Lap belts are found in many different types of vehicles throughout the world.
Although conventional lap belts are well used and accepted, they do not limit movement of an occupant""s head and torso. Thus, although the lower body is restrained, the upper body may experience rapid and dangerous movement during an accident. This is particularly dangerous for passengers in the front seat of an automobile, who may strike the steering wheel, dashboard, or windshield during an accident.
A seat belt having a shoulder strap limits an occupant""s upper body movement in an accident, providing improved and potentially lifesaving restraint. Shoulder-strap restraints come in various configurations, involving both single- and double-strap implementations. In one commonly employed shoulder-strap configuration, the seat belt webbing traverses the occupant""s upper body in a diagonal fashion, passes through a latch plate, and then traverses the occupant""s lap. The latch plate is fastened to a buckle, which is secured to the vehicle. This seat belt system is frequently employed in passenger vehicles and is frequently referred to as a three-point seat belt system.
However, in this configuration, problems arise in loading and unloading occupants. Often the latch plate becomes dislocated from its correct position, making it difficult for the occupant to locate the latch plate or correctly position the latch plate before engaging the seat belt.
Dislocation of the latch plate creates a number of safety and convenience issues. For example, the latch plate could move so far from its correct position that it may be difficult for the occupant to locate or secure the latch plate, discouraging the occupant from using the seat belt. Also, in this condition, the seat belt webbing is more likely to become knotted or entangled with other items around the seat belt. Further, if the latch plate is not in the correct position when in use, the seat belt webbing may have slack, preventing the seat belt from safely restraining the occupant during an accident.
Locking the latch plate into a fixed position relative to the seat belt webbing is one potential solution to the problems noted above. However, this solution has substantial limitations in certain scenarios. In a collision, the torso of the occupant is often thrust forward, applying great pressure to the torso portion of the seat belt webbing (the portion of the seat belt webbing above the latch plate). If the latch plate is locked into position relative to the seat belt webbing, the tension in the torso portion of the seat belt webbing will not be transferred to the lap portion of the seat belt webbing (the portion of the seat belt webbing below the latch plate). As a consequence, the lap portion of the seat belt webbing may be undesirably loose.
In this condition, the occupant""s lower body may strike portions of the vehicle or other objects with great force. Most dangerously, lacking tension in the lap portion of the seat belt webbing, the occupant may slide completely or partially out of the seat belt restraint (a process known as xe2x80x9csubmariningxe2x80x9d), resulting in potentially more serious injuries. The transfer of tension from the torso portion of the seat belt to the lap portion of the seat belt during an accident is desirable and enhances the restraining capabilities of the seat belt.
Thus, it would be an advancement in the art to provide a latch plate that maintains a fixed position relative to the seat belt webbing during normal usage, but enables movement of the seat belt webbing relative to the plate in the event of an accident.
Such a latch plate is disclosed and claimed herein.
The apparatus and methods of the present invention have been developed in response to the present state-of-the-art, and, in particular, in response to problems and needs in the art that have not yet been fully resolved by currently available inflatable seat belt systems. The present invention provides an apparatus for enhancing the effectiveness of seat belt systems. To achieve the foregoing, and in accordance with the invention as embodied and broadly described in the preferred embodiment, a breakaway latch plate is disclosed that maintains seat belt webbing at a fixed position relative to the plate during normal usage, but allows movement of the seat belt webbing relative to the latch plate during accident conditions.
In one embodiment, the breakaway latch plate may be used in connection with a three-point seat belt system. A three-point seat belt system may include seat belt webbing connected at one end to a torso retractor and at the other end to lap retractor.
The breakaway latch plate, which is coupled to the seat belt webbing, includes a latch plate body. More specifically, an interior surface of the latch plate body defines an orifice through which the seat belt webbing passes. The latch plate body includes a buckle interface that may interface with and be inserted into a buckle to secure the seat belt webbing across an occupant of the vehicle. When the buckle interface is secured to the buckle, a torso portion of the seat belt webbing diagonally traverses the occupant""s body, while a lap portion of the seat belt webbing crosses the occupant""s lap.
A locking mechanism is coupled to the latch plate body. The locking mechanism prevents movement of the seat belt webbing relative to the latch plate body when the locking mechanism is in a locked state. Conversely, when the locking mechanism is in an unlocked state, the locking mechanism permits movement of the seat belt webbing relative to the latch plate body.
The locking mechanism changes from the locked to the unlocked state in response to at least a predetermined load being applied to the seat belt webbing, such as during accident conditions. As a consequence, during an accident, tension in the torso portion of the seat belt webbing may be transferred to the lap portion of the seat belt webbing to provide additional restraint to an occupant""s legs and lower body.
The predetermined load required to change the breakaway latch plate from the locked to the unlocked state may be set by a manufacturer of the latch plate through, for instance, selection of materials of a particular strength to make the locking mechanism. Also, variations in the design of the locking mechanism contribute to setting the predetermined load required to change the plate into an unlocked state.
The locking mechanism may be embodied in various forms, four of which are disclosed herein. The disclosed embodiments are, of course, merely illustrative, not limiting of the scope of this invention.
The first embodiment includes a cam having a guide track, a pin opening, and a movable gripping mechanism. A guide pin, which is also attached the latch plate body, is disposed within the guide track. The guide track may be embodied in various forms, following both linear and nonlinear paths. In one embodiment, the guide track is sized just large enough to receive the guide pin, but to not permit the guide pin to move within the track.
A breakaway pin, which is attached to the latch plate body, is disposed within the pin opening. The breakaway pin is designed to break upon the application of at least a predetermined force to the pin.
The movable gripping mechanism (e.g., teeth) of the cam contacts and grips the seat belt webbing passing through the orifice when the locking mechanism is in a locked state. When a load is applied to the seat belt webbing, force is applied to the moveable gripping mechanism and cam. Consequently, force is applied to the breakaway pin. When the load is equal to or exceeds a predetermined load set by the manufacturer of the breakaway latch plate, the breakaway pin breaks and the cam (along with the movable gripping mechanism) rotates away from the seat belt webbing about the guide pin, permitting the seat belt webbing to move relative to the latch plate body.
In a second embodiment of the breakaway latch plate, the locking mechanism includes a locking pin. The interior surface, which defines the orifice through which the seat belt webbing passes, further defines a retention notch within the orifice. An aperture is disposed within the seat belt webbing.
The locking pin is disposed through the aperture in the seat belt webbing when the locking mechanism is in a locked state. In the locked state, the locking pin is also disposed, at one end, within the retention notch. The other end of the locking pin is attached to a hinged cam. The hinged cam is rotatably connected to the latch plate body.
When a load is applied to the seat belt webbing, the edges of the aperture exert force on the locking pin. If the applied load is equal to or greater than a predetermined load, the locking pin deforms and is displaced from both the retention notch and the aperture, permitting movement of the seat belt webbing relative to the latch plate body.
In a third embodiment of the breakaway latch plate, a locking pin, which is frangible, includes a first and a second end. The interior surface defining the orifice also defines at least one retention notch for receiving the first and second ends of the locking pin. Again, an aperture is disposed in the seat belt webbing.
In a locked state, the locking pin is disposed through the aperture of the seat belt webbing, and the first and second ends of the locking pin are retained within the one or more retention notches.
When a load is applied to the seat belt webbing, the edges of the aperture in the webbing exert force on the locking pin. As stated above, the locking pin is frangible. Consequently, when at least a predetermined load is applied to the seat belt webbing, the locking pin breaks so that the seat belt webbing may move relative to the latch plate body.
The fourth embodiment of the locking mechanism is similar to the third embodiment. However, instead of the locking pin being frangible, the retention notches are frangible. As a consequence, in a locked state, the locking pin passes through the aperture and the first and second ends of the locking pin are disposed within at least one frangible retention notch.
Again, when a load is applied to the seat belt webbing, the seat belt webbing at the edges of the aperture applies force to the locking pin and consequently to the frangible retention notches. When the predetermined load is applied to the seat belt webbing, the notch, rather than the locking pin, breaks to permit the seat belt webbing to move relative to the latch plate body.
In view of the foregoing, the breakaway latch plate offers advantages not present in conventional latch plates. The breakaway latch plate retains a fixed position relative to the seat belt webbing during normal usage. Thus, the latch plate may be conveniently accessed and used by an occupant. However, in accident conditions, the seat belt webbing may move with respect to the latch plate body, permitting tension from the torso portion of the seat belt webbing to be transferred to the lap portion of the seat belt webbing and vice versa.
These and other advantages of the present invention will become more fully apparent from the following description and appended claims, or maybe learned by the practice of the invention as set forth hereinafter.